Investigation on in vitro biodegradation behaviours of ZrO2-reinforced Mg-based metallic glasses

• Main Author: Ang, Chern Heidi
• Other Authors: Tan Ming Jen
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/53996
• Institution: Nanyang Technological University

Ageing population is a phenomenon faced by many countries across the world. This phenomenon sparked interests in the development of medical advances to keep up with the ageing society. Currently, the technology used for implantations requires the removal of the bio-medical devices after they have served their function. If the implants can be safely disintegrated into the human body after a certain period of time, this additional step of removing the implants can be eliminated. Mg alloys have been used to design biodegradable implants. However, its usage is restricted by its fast degradation rate in the physiological environment. In recent years, the development of Mg-based metallic glass provided a potentially better alternative material, compared to the crystalline Mg alloys for biodegradable implants. This project aims at investigating the biodegradation behaviours of ZrO2-reinforced Mg67Zn28Ca5 metallic glasses in physiological saline solution (PSS). Detailed characterisation tests were done on Mg67Zn28Ca5 metallic glass samples containing different concentrations of ZrO2, to investigate their corrosion behaviours. These tests include scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometer (ICP) and electrochemical tests. The presence of ZrO2 lead to more uniform corrosion as the surface roughness was more uniform in the samples with ZrO2. However, adding more that 8% of ZrO2 leads to the formation of cracks when the sample undergoes corrosion. This can be seen from the samples with higher percentages of ZrO2 disintegrating after a few days of immersion. It is also proven that adding more ZrO2 to the samples led to a more crystalline structure, which supports the tendency of cracks forming in the samples with more ZrO2. A passive layer is found to be formed on the samples after immersion. This formation of the passive layer increases as immersion time increases, and more of this layer can be observed with increased amount of ZrO2 in the sample. Adding ZrO2 to the samples slowed down the ion release rate of Mg, Zn and Ca ions. However, adding 16% or more concentration of ZrO2 can have adverse effects, increasing the ion release rate of the samples. The sample with 2% of ZrO2 showed a higher open circuit potential which indicates its higher resistance to corrosion, while adding more ZrO2 led to a reduction in corrosion resistance. Potentiodynamic polarization test reveals that the sample without ZrO2 has the least tendency to be corroded. However, the order of corrosion currents follows the order of 8% < 2% < 0% < 25% < 16% concentration of ZrO2. This suggests that the sample with 8% ZrO2 had the slowest corrosion rate. In summary, the presence of ZrO2 has significant influences on the corrosion behaviours of Mg67Zn28Ca5 metallic glass. In most of the characterization tests, the sample with 8% ZrO2 had the best results with reduced corrosion rate, while adding a higher percentage of ZrO2 led to increased corrosion rates.